Logistical passage measurement systems are used to collect logistical process information, permitting track and trace and statistical analyses. Radio frequency transponders are used in conjunction with strategically placed readers and antennas throughout a logistical process. One logistical object may be to identify the passage of objects, people, etc. The readers may be particularly useful at points of object exchange or at a point where an identifiable event occurs.
There are systems in place to collect automatically the time and position of an object automatically. This equipment is typically installed throughout industrial and commercial facilities and permits automated collection or measurement of time of arrival data. Equipment composed of antennas and readers are positioned at portals covering points of entry. Antenna and or multiple sets of antennas are position on the sides and in some cases on the top of the portal to permit the illumination of Radio Frequency tags in any orientation on a pallet or container coming through a portal. Antenna's are connected to a single reader and multiplexed in time illuminating RFID tags and processing reflected tag identification information. Alternatively multiple readers connected to one or more antenna covering the portal are synchronized to operate on different frequency channels to read tags passing through the portals. These existing systems operate at LF, HF and UHF frequencies where there is a direct relationship between the incident signal and reflected and or returned signal. Common problems with these types of systems include the reading of tags by adjacent readers. This phenomenon is referred to as cross reads by the Auto ID industry.
One approach to addressing the aforementioned problem is disclosed in U.S. Pat. No. 5,450,492 to Hook et al. The tag reader system of that disclosure relies on the independence of incident signal to the response—referred to in the industry as a dual frequency solution. There is no relationship in time between the incident and response signal. The response frequency is not derived from the incident frequency. This independence allows for communication or wake up of many tags entering a portal simultaneously. The simple wake up antennas preceding this art produced stationary magnetic fields, i.e. the magnetic field does not change direction in time for a specific point in space. However, Hook et al. does not fully address random tag orientation.
In applications where tag orientation is unpredictable the tags may be parallel with the field lines; in this case excitation, wake up, or turn on of the tags is difficult and often achieved by increasing radiated power to the maximum allowable limits to achieve acceptable results. Even with increased power there will still be areas within the foot print where some tags fail to turn on. Increasing the power to compensate for power creates large foot prints resulting in overlap in applications where dock doors are in close vicinity to one another. This is a common problem in current systems of today.
In order to improve portal response and eliminate or minimize cross reads the present invention uses a novel and innovative approach to creating an alternating magnetic field and magnetic vectors at necessary field strength within a given space to activate or turn on tags in any orientation within an exciter unit foot print.